1. Field of the Invention
The invention generally relates to a pixel structure, in particular, to a pixel structure characterized by a high aperture ratio and the reduced number of photomasks.
2. Description of Related Art
An organic light emitting diode (OLED) panel is a type of self-luminous display device. It has the advantages of a wide viewing angle, low power consumption, a simplified manufacturing process, low production costs, a wide operating temperature range, high response speed, full color display, etc. Due to these advantages, the OLED panel is expected to become the mainstream product for the next generation of flat panel displays. In general, the OLED panel includes a plurality of pixel structures, and each pixel structure further includes a plurality of active devices (for example, thin film transistors) or passive devices (for example, resistors and capacitors), a cathode or an anode electrically connected to the active devices, and an organic light emitting layer disposed between the anode and the cathode.
The active devices of the pixel structure can be manufactured by applying indium-gallium-zinc oxide (IGZO) techniques. IGZO is a type of metal oxide that contains indium, gallium and zinc and has a carrier mobility that is ten times higher than amorphous silicon (a-Si). Such type of metal oxides can greatly increase the speed of charging or discharging the pixel electrode by the active device, hence achieving fast frame rates and allowing smoother animation playback. Currently, as to the top-gate type of the pixel structure, seven photomasks are often used to maintain a high aperture ratio of the pixel structure. The high aperture ratio can improve the overall light emitting efficiency of the panel, hence making the panel more power efficient. However, excessive use of photomasks will increase the production costs and simultaneously reduce the volume of production.